linux-hardening - [PATCH] drm/dp: Fix off-by-one in register cache size

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Message-Id: <20211203084333.3105038-1-keescook@chromium.org>
Date:   Fri,  3 Dec 2021 00:43:33 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        Ankit Nautiyal <ankit.k.nautiyal@...el.com>,
        Uma Shankar <uma.shankar@...el.com>,
        Jani Nikula <jani.nikula@...el.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] drm/dp: Fix off-by-one in register cache size

The pcon_dsc_dpcd array holds 13 registers (0x92 through 0x9E). Fix the
math to calculate the max size. Found from a -Warray-bounds build:

drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_pcon_dsc_bpp_incr':
drivers/gpu/drm/drm_dp_helper.c:3130:28: error: array subscript 12 is outside array bounds of 'const u8[12]' {aka 'const unsigned char[12]'} [-Werror=array-bounds]
 3130 |         buf = pcon_dsc_dpcd[DP_PCON_DSC_BPP_INCR - DP_PCON_DSC_ENCODER];
      |               ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/drm_dp_helper.c:3126:39: note: while referencing 'pcon_dsc_dpcd'
 3126 | int drm_dp_pcon_dsc_bpp_incr(const u8 pcon_dsc_dpcd[DP_PCON_DSC_ENCODER_CAP_SIZE])
      |                              ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: e2e16da398d9 ("drm/dp_helper: Add support for Configuring DSC for HDMI2.1 Pcon")
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc: Maxime Ripard <mripard@...nel.org>
Cc: Thomas Zimmermann <tzimmermann@...e.de>
Cc: David Airlie <airlied@...ux.ie>
Cc: Daniel Vetter <daniel@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/drm/drm_dp_helper.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 30359e434c3f..472dac376284 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -456,7 +456,7 @@ struct drm_panel;
 #define DP_FEC_CAPABILITY_1			0x091   /* 2.0 */
 
 /* DP-HDMI2.1 PCON DSC ENCODER SUPPORT */
-#define DP_PCON_DSC_ENCODER_CAP_SIZE        0xC	/* 0x9E - 0x92 */
+#define DP_PCON_DSC_ENCODER_CAP_SIZE        0xD	/* 0x92 through 0x9E */
 #define DP_PCON_DSC_ENCODER                 0x092
 # define DP_PCON_DSC_ENCODER_SUPPORTED      (1 << 0)
 # define DP_PCON_DSC_PPS_ENC_OVERRIDE       (1 << 1)
-- 
2.30.2